The present invention relates to automatic transmissions and in particular to controlling peak pressures in automatic transmissions modified to operate at high pressures for use with increased torque.
There is a growing interest in high performance applications of vehicles with diesel engines. Such engines are being modified to produce between 1,000 and 4,000 foot pounds of torque or there about for tractor pull and drag racing events. Such high torque levels generally result in automatic transmission clutches slipping. To reduce such slipping, the transmissions are modified to increase the transmission fluid pressure in the transmissions. Normal fluid pressure is typically 85 PSI, and under throttle up to 240 PSI, briefly, but the pressures required to prevent slipping in the under up to 4,000 foot pounds of torque may be as high as 325 to 450 PSI.
Fluid pressure in the transmission may be raised by using a stiffer spring in the main pressure regulator. For example, during overhaul the main pressure regulator valve spring may be replaced to raise maximum fluid pressure from 85 PSI to 250 to 285 PSI. However, the main pressure regulator established a minimum pressure, and, for example, during a shift when a clutch might slip, the operating pressure is increased by the main mod line solenoid which momentarily raises the operating pressure by as much as 180 PSI by adding fluid pressure to the main pressure regulator spring pressure.
Each of the tractor pull and drag racing events require different engine settings, for example, some events benefit from very high torque output and other only require a lower torque output to be competitive. Running at high torque in every event requires greater engine maintenance and costs, and as a result, teams often run at lower torque levels. The lower torque levels allow lower pressure in the transmission which would also reduce transmission failures. The ability to run at lower torque levels may not be understood until the conditions at the events determined at the time of the event.
Unfortunately, known methods require replacing the main pressure regulator spring to adjust transmission pressure, and replacing the main pressure regulator spring requires removing the transmission which is often not feasible at an event.